Photodynamic Therapy (PDT) is emerging as a novel cancer treatment modality to help patients to live longer and to improve their quality of life without causing long-term side-effects. PDT is still failing to obtain deserved popularity in society due to current technological constraints and absence of practical advances as it is only offered in some treatment center and studied with little clinical trials. Recently, a renaissance of PDT has commenced with its wide recognition as a valuable treatment option for localized cancers (i.e. non-metastatic cancers), as well as pre-cancers of the skin and in the mouth, after three PDT photosensitizing agents have been approved by the United States Food and Drug Administration (FDA), e.g. Aminolevulinic acid (ALA). Nevertheless, conventional PDT still has from several limitations and drawbacks: (i) it is only able to treat diseased areas where light can be reached, that is, on or just under the skin; (ii) currently-used PDT drugs could leave people very sensitive to light, and therefore special precautions must be taken after the drugs are put in or on the body; (iii) adverse in-vitro/in-vivo reactions occur due to the variation in physiological conditions and notched distribution of cytotoxic singlet oxygen; and (iv) non-specific therapeutic nature may jeopardize normal cells during PDT treatment.
In this regard, porphyrin-based moieties, another novel class of promising PDT agents, have been investigated extensively by scientists worldwide to develop photodynamic therapy can be available and effective to other types of cancers and diseases particularly in the skin, bladder, mouth, and brain. As far as the light penetration depth for the singlet oxygen (1O2) generation is concerned, several porphyrin moieties have successfully showed the possibility to achieve near-infrared (NIR) excitation (via multi-photon/Second harmonic generation). NIR photons can penetrate deep and emit expeditiously from tissues without causing cell damage with their strong two-photon absorption properties being at ˜860 nm. In the literature and referenced patent filing, a porphyrinato metal complex is disclosed which can serve as an in-vivo anti-cancer torpedo equipped with visible-to-NIR emission for imaging and discriminating radar for tumor cell selectivity, and 1O2 explosive ammunition. However, the cancer selectivity of these PDT agents are still not yet solved and there exists a need to provide PDT agents with better cancer selectivity.
It is an objective of the present invention to provide for PDT probes that can specifically localize on particular tumors, and their PDT processes can be monitored via NIR emission.